Eagle Biology - Reproduction
The Dalliance of the Eagles
Skirting the river road, (my forenoon walk, my rest)
Skyward in air a sudden muffled sound, the dalliance of the eagles,
The rushing amorous contact high in space together
The clinching interlocking claws, a living, fierce, gyrating wheel,
Four beating wings, two beaks, a swirling mass tight grappling,
In tumbling turning clustering loops, straight downward falling,
Till o'er the river pois'd, the twain yet one, a moment's lull,
A motionless still balance in the air, then parting, talons loosing,
Upward again on slow-firm pinions slanting, their separate diverse flight,
She hers, he his, pursuing.
--- Walt Whitman, The Dalliance of the Eagles
Although Walt Whitman had never actually seen the bald eagle's courtship ritual called cartwheeling, he wrote The Dalliance of the Eagles based on the description a friend had given him of this extraordinary display.
Once attracted to a potential partner, the bald eagle may begin one of several elaborate courtship rituals called "cartwheeling." In this magnificient display, the eagles soar to dizzying heights, lock talons, and begin a breathtakingly death-defying plunge to the earth. Just moments before striking the ground, the eagles disengage and once again soar to the heavens. If the timing is not perfect, certain death awaits this pair of speeding bullets.
Eagles that are in combat with each other also may interlock their talons and fall in cartwheel fashion toward the ground. During the 1980s, this happened in Michigan with a first-year bald eagle (non-breeding) that had been hacked and released in Tennessee earlier that year. It fell to a highway, where it was hit by a truck and died from its injuries a few days later.
Other behaviors frequently observed in spring, the beginning of the eagle mating season, that may indicate courtship include pair perching, bill stroking and pecking, and overall body stroking with the bill.
As in many species, the female appears to initiate courtship by assuming a more passive stance and behavior than usual. Observers have also noted a single, high-pitched call only heard during courtship or the mating period.
Aerial chases in which the courting pair chase, roll, and fly upside down in pairs have been noted as well. To attract a mate, bald eagles have been seen to roller coaster. In this display, the eagle soars high into the air, folds its wings and dives toward the ground at a tremendous speed. Just before reaching the ground, the performer pulls up and begins the sequence again. This display is called the "roller coaster" because the series of flights resembles the path of a speeding amusement ride.
In the past, scientists believed that the bald eagle mated for life. In scientific terms, the bald eagle was considered monogamous, a word that comes from Latin - mono- meaning "one" or "single" and gamous from the root for "marriage." Today, scientists have new evidence that suggests that although bald eagles clearly tend to stay with one partner, some bald eagles do "divorce" and certainly bald eagles that have lost a partner "remarry."
Bald eagles mate when they reach sexual maturity at around four or five years of age. It is thought that the distinctive coloring (white head, bright yellow beak) of the adult bald eagle signals potential mating partners. It is not known how bald eagles select their mates, but scientists speculate that winter roosting sites where bald eagles uncharacteristically gather in large groups, may serve as bald eagle "meet markets".
Once attracted to a potential partner, the bald eagle may begin one of several elaborate courtship rituals called "cartwheeling." In this magnificent display, the eagles soar to dizzying heights, lock talons, and begin a breathtakingly death-defying plunge to the earth. Just moments before striking the ground, the eagles disengage and once again soar to the heavens. If the timing is not perfect, certain death awaits this pair of speeding bullets.
After this thrilling courtship, the bald eagle pair must mutually agree upon a nesting site. Since the natural tendency is for the bald eagle to return to the place of its first flight, or the location where the eagle first fledged, one of the pair must agree to a new home. Scientists are not able to predict which fledging site the pair will select and assume that somehow the decision is mutually agreed upon by the nesting pair.
Bald eagles typically lay eggs in wild Tennessee nests each season in late February, plus or minus about one month. Captive-breeding bald eagles typically lay their eggs in late March through April at the American Eagle Foundation of Pigeon Forge, TN. The eggs, called a clutch are protected by both parents, though the female eagle takes the major responsibility for incubating the eggs for the thirty-five days until they hatch. After hatching, both parents alternately hunt for food and feed the young. Young remain in the nest until about three months of age.
The next season, the nesting pair lay a new clutch of from one to three eggs and begin the process again.
The nesting season for bald eagles depends on where the bald eagle lives. Bald eagles that live in colder climates in the north will begin repairing and building their nests later than eagles living in warmer climates in the south. In a moderate climate, such as the one found in the state of Tennessee, bald eagles may begin their nesting season by early September. At this time, the eagles tend to increase their use of the nest site. Nests may be repaired during the months from October to January with most construction taking place in January and February. The same nest is usually used year after year. However, for insurance, bald eagles will generally build what is called a secondary nest within 350 yards of the primary, or first, nesting site.
The size of bald eagle nests are legendary. Tales are told of bald eagle nests weighing up to 2 to 3 tons! The nests reach such enormous sizes because the bald eagle continues to use the same nests over its lifetime. Since a bald eagle is not a small bird and requires a large nest to accomodate the male, female, and up to two or three young eaglets, the nests are rather large in the first place. Bald eagles may live up to thirty years of age in the wild, so a large nest which is expanded year after year for thirty years can become extremely large and heavy.
The huge size of the bald eagle nest suggests that the trees that contain eagle nests must have branches that will be able to support the weight of the nest. The materials that make up the nest include large sticks, sometimes as long as five feet. Bald eagles also seem fond of white pine and will often include at least of few sprigs of pine in every nest.
The inside of the nest is lined with soft materials collected by the bald eagles during its construction. The lining provides a comforting environment for baby chicks and eaglets. This interior section of the nest is usually 2-3 feet deep to prevent chicks and eaglets from falling from the nest. As the eaglets grow larger, this becomes a real danger and many juveniles fall to their deaths from high eagle nests each year.
Humans affect bald eagles most during the early stages of nesting activity. During that time period, bald eagles will quickly abandon a nest if humans are detected or some other disburbance occurs. This means that eagle chicks are frequently abandoned and this is one cause of the high eagle chick death rate.
Nests are placed in the tallest trees of the area. Bald eagles sometimes build their nests as high as 200 feet in the air. Generally, the nests are surrounded by dead limbs or sparse foliage. Scientists assume that this allows the bald eagle a clear flight path from the nest to its food source. Eagles typically nest in trees an average of 375 yards away from the water, but nests have been located as far away as 2 miles. The more human activity in an area, the further away the eagle nest will be. Nests are usually located 4 to 6 yards below the treetop under an umbrella of protective foliage.
The first flight of a bald eagle affects its life forever. Just as humans must pass certain cultural rites of passage in growing from childhood to adolescence to adulthood, the bald eagle must take its first flight away from the nest and learn to fend for itself in the wild before it finally takes on the plumage and the responsibilities of the adult eagle at about four or five years of age.
At about two months of age, the juvenile bald eagle has reached its full adult size. In fact, by this time the juvenile eagle actually weighs more and has more and longer feathers than an adult bald eagle. But despite its size, a bald eagle this age has not undergone its most signficant rite of passage: fledging. When a bald eagle fledges, it takes its first or maiden flight away from the nest.
Though the juvenile will continue to return to the nest for care and food supplements from its parents for several weeks, this first flight will have dramatic effects on the young eagle's life. The site of this first flight or fledging will be where the bald eagle later returns to nest and raise its own young.
After the bald eagle takes its first awkward flight at about three months of age, it will begin a four to five year period of learning to become an adult bald eagle. The new fledgling has many lessons to learn and will roam over large distances for four to five years, continually expanding its repertoire of flight, hunting, and basic survival skills.
As its skills improve, the young bald eagle's plumage and overall appearance gradually changes as well until it reaches sexual maturity at about four or five years of age. At this time the bald eagle acquires the distinctive white-headed plumage of adulthood. This physical change signals the beginning of a new phase for the bald eagle.
Now that the eagle has reached sexual maturity, it begins to search for a mate. Scientists believe that one reason for the dramatic physical changes in the bald eagle's appearance is to signal the readiness to mate. Scientists also think that bald eagles gather in large groups during their winter migrations to scout out potential partners. At any rate, once the bald eagles have decided to mate, they tend to remain faithful to their chosen partner.
When this partner is selected and spring or the breeding season approaches, the bald eagle pair begin to nest. The location of the nest has been predetermined. Upon reaching maturity, bald eagles return to nest within 75 miles of the site of their original flight. A bald eagle pair must jointly decide whether to return to the original home of the male or female bald eagle. Exactly how this is decided is not known, but it is guaranteed that the pair will return to the fledge site of either the male or female.
The fact that bald eagles tend to return to the region of their first flight to nest has been an important principle for recovery efforts to restore the bald eagle population in the United States. Scientists learned that bald eagles could be transported, either as young eaglets or as eggs, to different locations in the United States. As long as the bald eagles did not become dependent upon their human caregivers and were released in a suitable habitat, the bald eagles would return to the site of their first flight in four or five years to nest and raise their young. Using this principle based on fledging has enabled scientists to restore bald eagle populations even in places where bald eagles had not nested in over twenty years.
By learning more about bald eagle behaviors, scientists have been able to help the bald eagle begin to restore its numbers in places where it was once abundant. Though this principle is quite simple, actually providing for bald eagles' needs without allowing them to become dependent on human assistance, takes time, effort, and knowledge. To learn more about the bald eagle recovery process, visit the Eagle Recovery category of this Internet site.